o of the binary system. Therefore, If an electronIc machine were to store its data in decimal, it would need ten vacu- um tubes, or other bi-stable devices, to represent the ten possible values for an) one decimal place. Indeed, the ENIAC did use the decimal system in storing numbers. \VIth the advent of electronic machines, it became clear that bi-stable devices Were suited to storing binary di- rectly, and essentially all the machines that have followed the E I-\C have made use of binary numbers through- out. The use of binary greatly simplifies arithmetical processes in the machine Binary addition, for example, is very simple to translate in terms of electric circuits. 1 + 0 == 1 means that when a particular circuit, designed for add- ing, is fed one pulse, corresponding to aI, along wit.h no pulse, correspond- ing to a 0, it responds by producing one pulse, corresponding to a 1. MultI- plication in binary is equally easy. To see this, we have only to multiply 2 and 3 in binary-which means that We multIpl) the binary numbers 10 and 11: 11 10 00 11 110 The number ] 10, as we have seen, is the binary equivalent of 6. It is evident from this example that lTIultiplying the 11 b) the 0 in the 1 0 produces just zeros, while multiplying it by the 1 In the 10 produces the number 11 again. ThIs is characteristic of binary multIpli- cation, and makes the designing of mu]- tiplying circuits muc.h sImpler than it would he if the multiplication were done in decimal, in which each place in the product may have any of the ten values between 0 and 9. In the parlance of information theory, the fact that a bi-stable device is on or off is said to constitute a "bit" of in- formation. Thus, it takes at must four bits of information tu store a decimal digit in binary. ( For example, to store the number 8, which is 1 QuO in binar), clearly requIres four on-off registers, while the number 4, which is 100 in binary, requires three on-off units.) In the I.B.Y1. 7090 computer, to take d typical modern machine, information is stored In the memory in units of "words," each contaIning thirty-six bits. The 7090 can store approximate- ly thirty-three thousand words, whIch means that it can store about thirty- three thousand ten-digit numbers. Bab- bage planned to store in his Engine a thousand fifty-digit numbers. ThIs rep- New colours, new weights and a newly trim look? Or classic shades, weights and single pl<iats? Whichever you choose, the fashion is Daks trousers. Unique, self-supporting, recognized internationally for their impeccable hang and fit, Daks [rousers are as comfortable as only Sim pson tailors can make them. e Tryon Daks trousers See what they can do for you. In lightweight, long-lived British woollens. From $32.50. Slightly higher in the West e At fine stores across the country or \vnte Daks U.S.A. Inc. 1290 Avenue of the Americas, N ew York 19, N.Y. Dept. NY-13. Tailored by S. Simpson Ltd., London, England 75 f ( If , I f If I , , f ( \ If \ \ , ( \ \ J \ ' t' I \ I \ " \ , , I \ \ ( , \ , T · , :1"1 I 'I I /'1 I ,I ; ; " " I ,. I,' ,t, . ;'; , f r ' " t " 1"1 t.' t . ,I. f' . fit .. , I J. ,"." f '1 I, \ 'I '\. I, :r " JI' I U 1'1 1'1' ,;1 r , , , 'I " I J , , ,.,' ,. ) t .... . VOll $e rS " , ..